Research on the Modeling and Control Strategy of Offshore Wind Power Flexible DC Transmission System

Less harmonics, no commutation failure and no need for a great quantity of reactive power compensation are the advantages of flexible direct current transmission system. These advantages make it an effective way for far distance transmission of big capacity offshore wind energy. Modular multi-level converter (MMC) has a good performance in control and easy redundant expansion, which has attracted much attention in the far distance transmission of offshore wind energy. At present, there are few analysis of the MMC-HVDC system with double fed induction generator (DFIG) for the typical scenario of offshore wind energy flexible direct current transmission. This paper presents the topology of DFIG and MMC, and establishes their mathematical model respectively. The control block diagram of each module is given and the control strategy is studied and analyzed. Finally, the simulation model of MMC-HVDC delivery system with DFIG is built on PSCAD / EMTDC simulation platform, which proves the accuracy of mathematical model and feasibility of the control strategy in this paper.